Wiring Best Practices

Overview

This section describes the wiring guidelines and associated best practices to be respected when using the M241 Logic Controller system.

DANGER
	HAZARD OF ELECTRIC SHOCK, EXPLOSION OR ARC FLASH Disconnect all power from all equipment including connected devices prior to removing any covers or doors, or installing or removing any accessories, hardware, cables, or wires except under the specific conditions specified in the appropriate hardware guide for this equipment. Always use a properly rated voltage sensing device to confirm the power is off where and when indicated. Replace and secure all covers, accessories, hardware, cables, and wires and confirm that a proper ground connection exists before applying power to the unit. Use only the specified voltage when operating this equipment and any associated products. Failure to follow these instructions will result in death or serious injury.

DANGER

HAZARD OF ELECTRIC SHOCK, EXPLOSION OR ARC FLASH

Disconnect all power from all equipment including connected devices prior to removing any covers or doors, or installing or removing any accessories, hardware, cables, or wires except under the specific conditions specified in the appropriate hardware guide for this equipment.
Always use a properly rated voltage sensing device to confirm the power is off where and when indicated.
Replace and secure all covers, accessories, hardware, cables, and wires and confirm that a proper ground connection exists before applying power to the unit.
Use only the specified voltage when operating this equipment and any associated products.

Failure to follow these instructions will result in death or serious injury.

WARNING
	LOSS OF CONTROL The designer of any control scheme must consider the potential failure modes of control paths and, for certain critical control functions, provide a means to achieve a safe state during and after a path failure. Examples of critical control functions are emergency stop and overtravel stop, power outage and restart. Separate or redundant control paths must be provided for critical control functions. System control paths may include communication links. Consideration must be given to the implications of unanticipated transmission delays or failures of the link. Observe all accident prevention regulations and local safety guidelines.¹ Each implementation of this equipment must be individually and thoroughly tested for proper operation before being placed into service. Failure to follow these instructions can result in death, serious injury, or equipment damage.

WARNING

LOSS OF CONTROL

The designer of any control scheme must consider the potential failure modes of control paths and, for certain critical control functions, provide a means to achieve a safe state during and after a path failure. Examples of critical control functions are emergency stop and overtravel stop, power outage and restart.
Separate or redundant control paths must be provided for critical control functions.
System control paths may include communication links. Consideration must be given to the implications of unanticipated transmission delays or failures of the link.
Observe all accident prevention regulations and local safety guidelines.¹
Each implementation of this equipment must be individually and thoroughly tested for proper operation before being placed into service.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

¹ For additional information, refer to NEMA ICS 1.1 (latest edition), "Safety Guidelines for the Application, Installation, and Maintenance of Solid State Control" and to NEMA ICS 7.1 (latest edition), "Safety Standards for Construction and Guide for Selection, Installation and Operation of Adjustable-Speed Drive Systems" or their equivalent governing your particular location.

Wiring Guidelines

The following rules must be applied when wiring an M241 Logic Controller system:

I/O and communication wiring must be kept separate from the power wiring. Route these 2 types of wiring in separate cable ducting.
Verify that the operating conditions and environment are within the specification values.
Use proper wire sizes to meet voltage and current requirements.
Use copper conductors (required).
Use twisted pair, shielded cables for analog, and/or fast I/O.
Use twisted pair, shielded cables for networks, and fieldbus.

Use shielded, properly grounded cables for all analog and high-speed inputs or outputs and communication connections. If you do not use shielded cable for these connections, electromagnetic interference can cause signal degradation. Degraded signals can cause the controller or attached modules and equipment to perform in an unintended manner.

WARNING
	UNINTENDED EQUIPMENT OPERATION Use shielded cables for all fast I/O, analog I/O and communication signals. Ground cable shields for all analog I/O, fast I/O and communication signals at a single point¹. Route communication and I/O cables separately from power cables. Failure to follow these instructions can result in death, serious injury, or equipment damage.

¹Multipoint grounding is permissible (and in some cases inevitable) if connections are made to an equipotential ground plane dimensioned to help avoid cable shield damage in the event of power system short-circuit currents.

For more details, refer to Grounding Shielded Cables.

NOTE: Surface temperatures may exceed 60 °C (140 °F).

To conform to IEC 61010 standards, route primary wiring (wires connected to power mains) separately and apart from secondary wiring (extra low voltage wiring coming from intervening power sources). If that is not possible, double insulation is required such as conduit or cable gains.

Rules for Removable Screw Terminal Block

The following tables show the cable types and wire sizes for a 5.08 pitch removable screw terminal block (I/Os and power supply):

The use of copper conductors is required.

DANGER
	LOOSE WIRING CAUSES ELECTRIC SHOCK Tighten connections in conformance with the torque specifications. Failure to follow these instructions will result in death or serious injury.

DANGER
	FIRE HAZARD Use only the correct wire sizes for the maximum current capacity of the I/O channels and power supplies. For relay output (2 A) wiring, use conductors of at least 0.5 mm² (AWG 20) with a temperature rating of at least 80 °C (176 °F). For common conductors of relay output wiring (7 A), or relay output wiring greater than 2 A, use conductors of at least 1.0 mm² (AWG 16) with a temperature rating of at least 80 °C (176 °F). Failure to follow these instructions will result in death or serious injury.

DANGER

FIRE HAZARD

Use only the correct wire sizes for the maximum current capacity of the I/O channels and power supplies.
For relay output (2 A) wiring, use conductors of at least 0.5 mm² (AWG 20) with a temperature rating of at least 80 °C (176 °F).
For common conductors of relay output wiring (7 A), or relay output wiring greater than 2 A, use conductors of at least 1.0 mm² (AWG 16) with a temperature rating of at least 80 °C (176 °F).

Failure to follow these instructions will result in death or serious injury.

Removing the I/O Terminal Block

The following figure shows the removal of the I/O terminal block from the M241 Logic Controller:

Step	Action
1	Remove power from your controller.
2	Pull down the protective cache:
3	Press with a screwdriver through the terminal block front hole:
4	Remove the terminal block:

Protecting Outputs from Inductive Load Damage

Depending on the load, a protection circuit may be needed for the outputs on the controllers and certain modules. Inductive loads using DC voltages may create voltage reflections resulting in overshoot that will damage or shorten the life of output devices.

CAUTION
	OUTPUT CIRCUIT DAMAGE DUE TO INDUCTIVE LOADS Use an appropriate external protective circuit or device to reduce the risk of inductive direct current load damage. Failure to follow these instructions can result in injury or equipment damage.

If your controller or module contains relay outputs, these types of outputs can support up to 240 Vac. Inductive damage to these types of outputs can result in welded contacts and loss of control. Each inductive load must include a protection device such as a peak limiter, RC circuit or flyback diode. Capacitive loads are not supported by these relays.

WARNING
	RELAY OUTPUTS WELDED CLOSED Always protect relay outputs from inductive alternating current load damage using an appropriate external protective circuit or device. Do not connect relay outputs to capacitive loads. Failure to follow these instructions can result in death, serious injury, or equipment damage.

AC-driven contactor coils are, under certain circumstances, inductive loads that generate pronounced high-frequency interference and electrical transients when the contactor coil is de-energized. This interference may cause the logic controller to detect an I/O bus error.

WARNING
	CONSEQUENTIAL LOSS OF CONTROL Install an RC surge suppressor or similar means, such as an interposing relay, on each TM3 expansion module relay output when connecting to AC-driven contactors or other forms of inductive loads. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Protective circuit A: this protection circuit can be used for both AC and DC load power circuits.

C Value from 0.1 to 1 μF

R Resistor of approximately the same resistance value as the load

Protective circuit B: this protection circuit can be used for DC load power circuits.

Use a diode with the following ratings:

Reverse withstand voltage: power voltage of the load circuit x 10.
Forward current: more than the load current.

Protective circuit C: this protection circuit can be used for both AC and DC load power circuits.

In applications where the inductive load is switched on and off frequently and/or rapidly, ensure that the continuous energy rating (J) of the varistor exceeds the peak load energy by 20 % or more.